This invention relates to seismic reflection exploration methods and is particularly adapted for (though not restricted to) use in such exploration under water, i.e. marine seismic exploration.
Such exploration involves the collection of data (arrival times of seismic wave trains) which define subsurface geological formations, due to reflections of seismic (sound) waves from such formations. It is well known that such data are obtained by producing a seismic disturbance at a source, for example, by detonating a charge of explosive, dropping a weight, actuating a vibrator, etc., and recording the resultant reflected seismic waves arriving at a plurality of receptors (a kind of microphone). Unfortunately, such waves are not the only waves produced; in fact, there are both random waves caused by wind, traffic or the like, and unwanted waves due to the production of the seismic disturbance (called source-generated waves) which interfere with reception of the desired reflections. A wide variety of methods have been produced for minimizing the reception of the undesired waves compared to those from the reflecting horizons. In fact, it has been made possible through various arrays of equipment and also through processing the data, for example, through large scale computers, to produce resultant records with the desired waves enhanced compared to all of the others present.
The current invention involves the use of arrays either for receiving seismic waves directionally at desired angles compared to the array, or as a source for producing seismic waves directionally in configurations which tend to minimize undesired waves. These directional responses are substantially the same for all seismic frequencies.
The first publication relating to this particular type of technique is an article by Fail and Grau, "Les Filtres en Eventail", Geophysical Prospecting Vol. 11 (1963) pp. 131-163. This was followed by: Embree, Burg and Backus "Wide-Band Velocity Filtering--The Pie Slice Process", Geophysics Vol. 28 (1963) pp. 948-974, and Treitel, Shanks and Frasier, "Some Aspects of Fan Filtering", Geophysics Vol. 32 (1967) pp. 789-800.